networkd: guard against NULL pointers

[thirdparty/systemd.git] / README

systemd System and Service Manager

DETAILS:
        http://0pointer.de/blog/projects/systemd.html

WEB SITE:
        http://www.freedesktop.org/wiki/Software/systemd

GIT:
        git://anongit.freedesktop.org/systemd/systemd
        ssh://git.freedesktop.org/git/systemd/systemd

GITWEB:
        http://cgit.freedesktop.org/systemd/systemd

MAILING LIST:
        http://lists.freedesktop.org/mailman/listinfo/systemd-devel
        http://lists.freedesktop.org/mailman/listinfo/systemd-commits

IRC:
        #systemd on irc.freenode.org

BUG REPORTS:
        https://bugs.freedesktop.org/enter_bug.cgi?product=systemd

AUTHOR:
        Lennart Poettering
        Kay Sievers
        ...and many others

LICENSE:
        LGPLv2.1+ for all code
        - except sd-readahead.[ch] which is MIT
        - except src/shared/MurmurHash2.c which is Public Domain
        - except src/shared/siphash24.c which is CC0 Public Domain
        - except src/journal/lookup3.c which is Public Domain
        - except src/udev/* which is (currently still) GPLv2, GPLv2+

REQUIREMENTS:
        Linux kernel >= 3.0
        Linux kernel >= 3.3 for loop device partition support features with nspawn
        Linux kernel >= 3.8 for Smack support

        Kernel Config Options:
          CONFIG_DEVTMPFS
          CONFIG_CGROUPS (it's OK to disable all controllers)
          CONFIG_INOTIFY_USER
          CONFIG_SIGNALFD
          CONFIG_TIMERFD
          CONFIG_EPOLL
          CONFIG_NET
          CONFIG_SYSFS
          CONFIG_PROC_FS
          CONFIG_FHANDLE (libudev, mount and bind mount handling)

        Udev will fail to work with the legacy layout:
          CONFIG_SYSFS_DEPRECATED=n

        Legacy hotplug slows down the system and confuses udev:
          CONFIG_UEVENT_HELPER_PATH=""

        Userspace firmware loading is deprecated, will go away, and
        sometimes causes problems:
          CONFIG_FW_LOADER_USER_HELPER=n

        Some udev rules and virtualization detection relies on it:
          CONFIG_DMIID

        Support for some SCSI devices serial number retrieval, to
        create additional symlinks in /dev/disk/ and /dev/tape:
          CONFIG_BLK_DEV_BSG

        Optional but strongly recommended:
          CONFIG_IPV6
          CONFIG_AUTOFS4_FS
          CONFIG_TMPFS_POSIX_ACL
          CONFIG_TMPFS_XATTR
          CONFIG_SECCOMP

        For systemd-bootchart, several proc debug interfaces are required:
          CONFIG_SCHEDSTATS
          CONFIG_SCHED_DEBUG

        For UEFI systems:
          CONFIG_EFIVAR_FS
          CONFIG_EFI_PARTITION

        Note that kernel auditing is broken when used with systemd's
        container code. When using systemd in conjunction with
        containers, please make sure to either turn off auditing at
        runtime using the kernel command line option "audit=0", or
        turn it off at kernel compile time using:
          CONFIG_AUDIT=n
        If systemd is compiled with libseccomp support on
        architectures which do not use socketcall() and where seccomp
        is supported (this effectively means x86-64 and ARM, but
        excludes 32bit x86!), then nspawn will now install a
        work-around seccomp filter that makes containers boot even
        with audit being enabled. This works correctly only on kernels
        3.14 and newer though. TL;DR: turn audit off, still.

        glibc >= 2.14
        libcap
        libseccomp >= 1.0.0 (optional)
        libblkid >= 2.20 (from util-linux) (optional)
        libkmod >= 15 (optional)
        PAM >= 1.1.2 (optional)
        libcryptsetup (optional)
        libaudit (optional)
        libacl (optional)
        libattr (optional)
        libselinux (optional)
        liblzma (optional)
        libgcrypt (optional)
        libqrencode (optional)
        libmicrohttpd (optional)
        libpython (optional)
        make, gcc, and similar tools

        During runtime, you need the following additional
        dependencies:

        util-linux >= v2.19 (requires fsck -l, agetty -s),
                      v2.21 required for tests in test/
        dbus >= 1.4.0 (strictly speaking optional, but recommended)
        sulogin (from util-linux >= 2.22 or sysvinit-tools, optional but recommended,
                 required for tests in test/)
        dracut (optional)
        PolicyKit (optional)

        When building from git, you need the following additional
        dependencies:

        docbook-xsl
        xsltproc
        automake
        autoconf
        libtool
        intltool
        gperf
        gtkdocize (optional)
        python (optional)
        python-lxml (optional, but required to build the indices)
        sphinx (optional)

        When systemd-hostnamed is used, it is strongly recommended to
        install nss-myhostname to ensure that, in a world of
        dynamically changing hostnames, the hostname stays resolvable
        under all circumstances. In fact, systemd-hostnamed will warn
        if nss-myhostname is not installed.

        To build HTML documentation for python-systemd using sphinx,
        please first install systemd (using 'make install'), and then
        invoke sphinx-build with 'make sphinx-<target>', with <target>
        being 'html' or 'latexpdf'. If using DESTDIR for installation,
        pass the same DESTDIR to 'make sphinx-html' invocation.

USERS AND GROUPS:
        Default udev rules use the following standard system group
        names, which need to be resolvable by getgrnam() at any time,
        even in the very early boot stages, where no other databases
        and network are available:

        tty, dialout, kmem, video, audio, lp, floppy, cdrom, tape, disk

        During runtime, the journal daemon requires the
        "systemd-journal" system group to exist. New journal files will
        be readable by this group (but not writable), which may be used
        to grant specific users read access.

        It is also recommended to grant read access to all journal
        files to the system groups "wheel" and "adm" with a command
        like the following in the post installation script of the
        package:

        # setfacl -nm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/

        The journal gateway daemon requires the
        "systemd-journal-gateway" system user and group to
        exist. During execution this network facing service will drop
        privileges and assume this uid/gid for security reasons.

WARNINGS:
        systemd will warn you during boot if /etc/mtab is not a
        symlink to /proc/mounts. Please ensure that /etc/mtab is a
        proper symlink.

        systemd will warn you during boot if /usr is on a different
        file system than /. While in systemd itself very little will
        break if /usr is on a separate partition, many of its
        dependencies very likely will break sooner or later in one
        form or another. For example, udev rules tend to refer to
        binaries in /usr, binaries that link to libraries in /usr or
        binaries that refer to data files in /usr. Since these
        breakages are not always directly visible, systemd will warn
        about this, since this kind of file system setup is not really
        supported anymore by the basic set of Linux OS components.

        systemd requires that the /run mount point exists. systemd also
        requires that /var/run is a a symlink → /run.

        For more information on this issue consult
        http://freedesktop.org/wiki/Software/systemd/separate-usr-is-broken

        To run systemd under valgrind, compile with VALGRIND defined
        (e.g. ./configure CPPFLAGS='... -DVALGRIND=1'). Otherwise,
        false positives will be triggered by code which violates
        some rules but is actually safe.